Mechanosynthesis and Mechanosynthesis Terminology
Atomic Force Microscopes (AFM) and similar devices (e.g., SFM, SPM, STM) have long been used to move individual atoms or molecules to precise locations. Early experiments included the use of atoms or molecules to create patterns on surfaces, or to cause chemical reactions. Examples of such work include (Meyer, Neu et al., “Building Nanostructures by Controlled Manipulation of Single Atoms and Molecules with the Scanning Tunneling Microscope,” Phys Stat Sol, 1995; Bartels, Meyer et al., “Basic Steps of Lateral Manipulation of Single Atoms and Diatomic Clusters with an Scanning Tunneling Microscope Tip,” Physical Review Letters, 4, 1997; Bartels, Meyer et al., “Controlled vertical manipulation of single CO molecules with the scanning tunneling microscope: A route to chemical contrast,” Applied Physics Letters, 2, 1997; Hla, Bartels et al., “Inducing All Steps of a Chemical Reaction with the Scanning Tunneling Microscope Tip: Towards Single Molecule Engineering,” PHYSICAL REVIEW LETTERS, 13, 2000).
Early experiments generally did not involve creating covalent bonds, or if they did, the reactions were electron-induced rather than caused by physical force. Subsequently, it became possible to use precise physical positioning and, if necessary, force, to make or break bonds; this is called mechanosynthesis. Mechanosynthesis was experimentally demonstrated in 2003 (Oyabu, Custance et al., “Mechanical vertical manipulation of selected single atoms by soft nanoindentation using near contact atomic force microscopy,” Phys. Rev. Lett., 17, 2003).
While early experimental work makes it clear that SPM equipment has long sufficed for basic mechanosynthesis, over time, SPM equipment and related metrology capabilities have become more sophisticated. For example, picometer-level distance measurement has been shown to be possible over long distances. (Lawall, “Fabry-Perot metrology for displacements up to 50 mm,” J. Opt. Soc. Am. A, 12, OSA, 2005) And, in addition to literature describing the custom fabrication of multi-probe SPMs (Eder, Kotakoski et al., “Probing from both sides: reshaping the graphene landscape via face-to-face dual-probe microscopy,” Nano Letters, 5, 2013), various vendors sell systems that have either more than one probe, or the ability to swap tips on a single probe. For example:
The MultiView 4000 (NANONICS IMAGING LTD. HEADQUARTERS, Israel), which can employ up to 4 probes with a scanner resolution of 0.02 Angstroms in the Z axis, and 0.05 Angstroms in the X and Y axis, the “Titanium” (NT-MDT Co., Building 100, Zelenograd, Moscow 124482, Russia), which has a cartridge that can automatically swap between 38 tips and offers <30 pm (0.3 Angstrom) scanner noise in X, Y, and Z, and the LT QuadraProbe™ (RHK Technology, Inc, Troy, Mich. 48083 USA) which includes 4 probes, each probe providing atomic resolution.
Several authors have explored the idea of atomically-precise manufacturing (Drexler, “Engines of Creation: The Coming Era of Nanotechnology,” Anchor, 1987; Drexler, “Nanosystems: Molecular Machinery, Manufacturing, and Computation,” New York, John Wiley & Sons, 1992; Freitas, “Nanomedicine, Volume I: Basic Capabilities,” Landes Bioscience, 1999; “Nanomedicine, Vol. IIA: Biocompatibility,” Landes Bioscience, 2003). But, despite long-standing conjecture and theoretical work in the field, mechanosynthesis has largely been treated as a laboratory curiosity due to the challenges that need to be addressed in order to develop it into a useful manufacturing technology.
The present invention describes methods, systems and products relating to the use of mechanosynthesis to manufacture atomically-precise structures. The structures are referred to as workpieces, and the workpieces are built using atoms (including groups of atoms or molecules) as raw material. These atoms are referred to as feedstock. Workpieces are built using tips to move feedstock atoms into desired locations on a workpiece, to remove undesired atoms from the workpiece, or to alter the bond structure of the workpiece. The positional control and force required for the tips can be supplied by a scanning probe microscope or variation thereof, or any other appropriate device, including devices built specifically for the purposes of mechanosynthesis, rather than microscopes adapted to that purpose.
The order in which atom and bonds are added, removed, or altered during the course of building a workpiece is referred to as a build sequence. A build sequence also encompasses the concept of a trajectory, which is the path along which an atom moves during a mechanosynthetic reaction. By using tips to move feedstock along a trajectory, to a specific location with respect to a workpiece, and then applying mechanical force as needed to bond the atom into position (or facilitate other reactions, such as the removal of atoms or rearrangement of bonds), atomically-precise workpieces can be manufactured.
Tips Used in Mechanosynthesis
The mechanosynthesis processes described herein use ultra-sharp tips designed to move atoms with sub-angstrom precision and to facilitate different reactions with those atoms. The tips may be, but do not have to be, atomically-precise. While some embodiments of the invention use atomically-precise tips, others do not. For example, a bootstrap sequence is presented herein which allows the creation of atomically-precise tips using non-atomically-precise tips.
Atomically imprecise, but ultra-sharp tips, also called probes, are available commercially (e.g., from Nanotools Gmbh, Munich, Germany; NANOSENSORS, Neuchatel, Switzerland; or NanoAndMore GMBH, Lady's Island, S.C. USA), or can be made using electron-beam induced deposition (EBID), among others techniques. (Tay and Thong, “Fabrication of super-sharp nanowire atomic force microscope using a field emission induced growth technique,” Review of Scientific Instruments, 10, 2004) Such tips can serve as a starting point for the bootstrap process described herein. Other tips available include carbon nanotube-based tips which can be functionalized to perform various reactions (Balasubramanian and Burghard, “Chemically functionalized carbon nanotubes,” Small, 2, 2005; Herman, “Toward Mechanosynthesis of Diamondoid Structures: IX Commercial Capped CNT Scanning Probe Microscopy Tip as Nowadays Available Tool for Silylene Molecule and Silicon Atom Transfer,” Journal of Computational and Theoretical Nanoscience, 12, 2012; “Toward Mechanosynthesis of Diamondoid Structures: X. Commercial Capped CNT SPM Tip as Nowadays Available C2 Dimer Placement Tool for Tip-Based Nanofabrication,” Journal of Computational and Theoretical Nanoscience, 9, 2013) and atomically-sharp tips created using field assisted etching (Rezeq, Pitters et al., “Nano-tip fabrication by spatially controlled etching,” U.S. Pat. No. 7,431,856, 2008; Pitters, Urban et al., “Method of fabricating nanotips with controlled profile,” US Patent App 20140231379, 2014).
In general, the important characteristic of a tip is that it reliably performs the desired mechanosynthetic reaction. Atomic precision is a helpful characteristic of tips for mechanosynthesis because knowing the precise placement of atoms on the tip allows the design of reliable reactions. This is not to say that atomically imprecise tips could not be used in mechanosynthesis processes (as the bootstrap process discussed herein demonstrates), for example, by characterizing each tip before use, by designing reactions where variation at the tip does not substantially affect the intended reactions, or by designing procedures which result in minimal tip-to-tip variation when preparing tips. However, the focus herein is on the use of atomically-precise tips (after bootstrapping).
Note that “tips” and “workpieces” are discussed extensively herein. However, defining one structure as a tip and another as a workpiece can be arbitrary in some circumstances. For example, when a tip removes a hydrogen atom from a workpiece, one might also say that the workpiece donated a hydrogen atom to the tip, logically reversing their roles. This distinction may seem pedantic, but can be meaningful in some situations such as recharging a tip (by adding feedstock, removing waste atoms, or both), or using one set of tips to build another set of tips. In such instances, a tip could be seen as the workpiece.
Enabling Technologies
Mechanosynthesis equipment, process, and workpiece design is largely based upon the confluence of atomic microscopy and computational chemistry. Microscopy techniques such as Scanning Probe Microscopy (SPM), Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM) have led to the ability to image and manipulate individual atoms, while computational chemistry has led to the ability to model structures which can be built by manipulating atoms, as well as the reactions used to build the structures, and the tools required to carry out the reactions.
The ability to perform robust mechanosynthesis requires that one be able to position atoms (generally with sub-angstrom precision), that one be able to apply mechanical force to an atom in a specific direction to cause the making or breaking of bonds, that one be able to design a desired workpiece with atomic precision, that one be able to calculate trajectories which will result in successful mechanosynthetic reactions, and that one possess, or be able to design, tips to carry out the intended reactions.
In addition to this list of necessities, it would be beneficial to be able to calculate the likelihood of pathological side reactions during mechanosynthetic reactions (the likelihood that, for example, a feedstock atom bonds to a workpiece atom adjacent to the intended target atom), the likelihood of pathological rearrangements before, during, or after a mechanosynthetic reaction, and to have control of the reaction environment (e.g., to make sure that it is inert with respect to the reactions being used and kept at an appropriate temperature).
Herein are describe methods, products and systems for addressing each one of these issues, taking mechanosynthesis from a laboratory curiosity to an actual manufacturing technology.
Computational Chemistry in Mechanosynthesis
Computational chemistry techniques can be very accurate. However, even on powerful computers, simulating large numbers of atoms at high levels of theory, and potentially using multi-scale techniques (e.g., ONIOM), multiple algorithms to “sanity check” results, and large basis sets, can be extremely computationally-demanding. However, an entire mechanosynthetic system need not be simulated at a high level of detail. Mechanosynthesis can be carried out in a more controlled environment than, for example, traditional liquid or gas phase chemistry, or biology experiments, resulting in the ability to simplify simulations by reducing the number of atoms which are simulated at high levels of detail.
In mechanosynthesis only a few, positionally-controlled atoms are participating in a reaction at any given time. Most reactions away from the intended reaction site can be prevented by the use of positional control, an inert environment, or appropriate temperatures. Therefore, the number of atoms that are directly relevant to a given reaction and thus must be simulated with high fidelity is quite small compared to the overall mechanosynthetic system or to other common settings in which chemical reactions take place. As a result, it is feasible to use computational chemistry techniques to simulate mechanosynthetic systems and reactions accurately enough to make reliable predictions about the behavior of those systems and reactions.
Software and Mechanosynthesis
Automation of AFM equipment and the like has long been possible, for example, via the common LabView software. Simple automation can reduce the need for a human operator to perform large numbers of reactions manually.
Software can also be used to enhance the positioning means of mechanosynthesis equipment. For example, even when a microscope has the requisite accuracy over short distances, it is possible that the accuracy degrades over longer distances. This can be due to multiple factors, such as non-linearity of piezo actuator responses, or thermal expansion. Sophisticated metrology can help address such issues, but software can also be used.
Software can be used to model the equipment, in many degrees of freedom, correcting for many sources of error. (Ceria, Ducourtieux et al., “Estimation of the measurement uncertainty of LNE's metrological Atomic Force Microscope using virtual instrument modeling and Monte Carlo Method,” 2015)
Software can also be used to carry out image recognition of a scanned surface, allowing the location of a tip to be determined based on the observed surface features, rather than relying only on, e.g., metrology feedback or dead-reckoning. (Celotta, Balakirsky et al., “Invited Article: Autonomous assembly of atomically perfect nanostructures using a scanning tunneling microscope,” Rev Sci Instrum, 12, 2014)
Element Grouping and Simulation
When referring to groups of elements herein, groups used include metals, non-metals, noble gases, transuranic elements, stable elements (defined as non-radioactive isotopes and isotopes with half-lives long enough to support the manufacturing and use of a product), or other logical groupings. The rationale behind these groupings would be obvious to one skilled in the art: generally the distinction is one of chemical properties (e.g., those in the same family on the periodic table or with the same valence), simulation feasibility, or practicality (e.g., safety aside, creating a device using isotopes with very short half-lives could pose problems in manufacturing and use of a device before the isotopes decay). In instances where a seemingly-arbitrary group of elements is specified, this is generally because reactions have been simulated using the elements in the group. This will be clear from the data presented herein.
Discussion of the Literature
The literature contains several examples of the computational analysis of mechanosynthesis, as well as experimental mechanosynthesis. However, this work tends to treat mechanosynthesis as a laboratory curiosity rather than attempting to address the issues inherent in creating a viable manufacturing technology. For example, the experimental literature is generally limited to decorating or modifying surfaces, and limited to small numbers of reactions.
No three-dimensional structures have been built. Further, in many previous examples of mechanosynthesis, there is a lack of separation of feedstock, presentation surface and workpiece (the presentation surface often serves as all three). And, the literature teaches only a small, non-generalizable set of tools and reactions, and uses atomically-imprecise tips, with no bootstrap process to facilitate the transition to atomically-precise tips. The computational literature contains other limitations. The literature is reviewed below with comments that will be helpful to not only understand the state of the art, but to distinguish it from the current invention.
Note that none of the literature cited herein is admitted as prior art. In fact, while some of the literature is cited to put the current invention in context because it demonstrates other ways of creating simple workpieces, mechanosynthesis may not even be employed, or the literature may not be analogous to the invention for other reasons.
Feedstock, Presentation Surface and Workpiece Terminology
The literature frequently uses the same entity as the “feedstock,” “presentation surface” and “workpiece.” As a result, these items are frequently not distinguished in the literature as separate entities, nor are they necessarily referred to by the same names as used herein. This occurs when, for example, an atom is removed from a surface, and then placed back onto that same surface. In such an example, the top layer of the presentation surface is also the feedstock and the workpiece. This severely limits the versatility of the workpieces that can be manufactured, constraining the elements used in reactions and the nature of the workpieces to which they are applied.
Previous Computational Simulations of Mechanosynthesis
Atomically-precise structures have been designed, and computationally examined. For example, see (Drexler, “Engines of Creation: The Coming Era of Nanotechnology,” Anchor, 1987; Drexler, “Nanosystems: Molecular Machinery, Manufacturing, and Computation,” New York, John Wiley & Sons, 1992). Computational techniques have also been used to design and validate mechanosynthetic reactions and tools (Mann, Peng et al., “Theoretical Analysis of Diamond Mechanosynthesis. Part II. C2 Mediated Growth of Diamond C(110) Surface via Si/Ge-Triadamantane Dimer Placement Tools,” JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, 2004; Peng, Freitas et al., “Theoretical Analysis of Diamond Mechanosynthesis. Part I. Stability of C2 Mediated Growth of Nanocrystalline Diamond C(110) Surface,” JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, 2004; Peng, Freitas et al., “Theoretical Analysis of Diamond Mechanosynthesis. Part III. Positional C2 Deposition on Diamond C(110) Surface using Si/Ge/Sn-based Dimer Placement Tools,” J. Comput. Theor. Nanosci, 2006; Temelso, Sherrill et al., “High-level Ab Initio Studies of Hydrogen Abstraction from Prototype Hydrocarbon Systems,” J. Phys. Chem. A, 2006; Temelso, Sherrill et al., “Ab Initio Thermochemistry of the Hydrogenation of Hydrocarbon Radicals Using Silicon, Germanium, Tin and Lead Substituted Methane and Isobutane,” J. Phys. Chem. A 2007; Freitas and Merkle, “A Minimal Toolset for Positional Diamond Mechanosynthesis,” Journal of Computational and Theoretical Nanoscience, 5, 2008; “Positional Diamondoid Mechanosynthesis” U.S. Pat. No. 8,171,568, 2009; Tarasov, Akberova et al., “Optimal Tooltip Trajectories in a Hydrogen Abstraction Tool Recharge Reaction Sequence for Positionally Controlled Diamond Mechanosynthesis,” J. Comput. Theor. Nanosci., 2, 2010).
However, each of these references suffers from important limitations in terms of being able to actually manufacture a workpiece via mechanosynthesis (which is not a criticism per se; this was not the intent behind these investigations). Such limitations include insufficient simulation detail or accuracy (e.g., not describing the computations in a manner that makes them reproducible, or using unrealistically-low levels of theory which cannot be assumed to provide reliable results), lack of a bootstrap sequence, lack of a comprehensive set of reactions and tips, lack of workpiece build sequences (or the means to create them), and others.
Literature is Surface-Based
In the literature mechanosynthesis is generally performed on, or to, a surface. For example, making and breaking of covalent bonds using mechanosynthesis via atomic force microscopy (AFM) was demonstrated for silicon atoms on a silicon surface. The AFM tip was used to remove, and re-deposit, Si atoms from the surface. (Oyabu, Custance et al., “Mechanical vertical manipulation of selected single atoms by soft nanoindentation using near contact atomic force microscopy,” Phys. Rev. Lett., 17, 2003)
Subsequently, other demonstrations of mechanosynthesis have included manipulation of silicon atoms on a silicon/oxygen surface (Morita, Sugimoto et al., “Atom-selective imaging and mechanical atom manipulation using the non-contact atomic force microscope,” J. Electron Microsc., 2, 2004), manipulation of germanium atoms on germanium surfaces (Oyabu, Custance et al., “Mechanical Vertical Manipulation of Single Atoms on the Ge(111)-c(2×8) Surface by Noncontact Atomic Force Microscopy,” Seventh International Conference on non-contact Atomic Force Microscopy, Seattle, Wash., 2004), manipulation of polymers on silicon surfaces (Duwez, Cuenot et al., “Mechanochemistry: targeted delivery of single molecules,” Nature Nanotechnology, 2, 2006), manipulation of silicon and tin atoms on a silicon surface (Sugimoto, Pou et al., “Complex Patterning by Vertical Interchange Atom Manipulation Using Atomic Force Microscopy,” Science, 2008), and the creation of 1-dimensional copper wires on a copper surface (Lagoute, Liu et al., “Electronic properties of straight, kinked, and branchedCu/Cu(111)quantum wires: A low-temperature scanning tunneling microscopy and spectroscopy study,” Physical Review B, 12, 2006).
Each of these references describe simple, surface-based 1 or 2-dimensional structures, made with a very limited number of reactions and feedstock. They do not teach a generalizable way of creating atomically-precise workpieces.
Mechanosynthesis Tools in the Literature
Prior to (Freitas and Merkle, “Positional Diamondoid Mechanosynthesis” U.S. Pat. No. 8,171,568, 2009), few tools for mechanosynthesis had been described in the literature. Those that had been described include various high-level descriptions of possible mechanosynthesis reactions (Drexler, “Nanosystems: Molecular Machinery, Manufacturing, and Computation,” New York, John Wiley & Sons, 1992), a hydrogen abstraction tool (Temelso, Sherrill et al., “High-level Ab Initio Studies of Hydrogen Abstraction from Prototype Hydrocarbon Systems,” J. Phys. Chem. A, 2006), a hydrogen donation tool (Temelso, Sherrill et al., “Ab Initio Thermochemistry of the Hydrogenation of Hydrocarbon Radicals Using Silicon, Germanium, Tin and Lead Substituted Methane and Isobutane,” J. Phys. Chem. A 2007), and dimer placement tools (Mann, Peng et al., “Theoretical Analysis of Diamond Mechanosynthesis. Part II. C2 Mediated Growth of Diamond C(110) Surface via Si/Ge-Triadamantane Dimer Placement Tools,” JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, 2004; Peng, Freitas et al., “Theoretical Analysis of Diamond Mechanosynthesis. Part I. Stability of C2 Mediated Growth of Nanocrystalline Diamond C(110) Surface,” JOURNAL OF COMPUTATIONAL AND THEORETICAL NANOSCIENCE, 2004; Peng, Freitas et al., “Theoretical Analysis of Diamond Mechanosynthesis. Part III. Positional C2 Deposition on Diamond C(110) Surface using Si/Ge/Sn-based Dimer Placement Tools,” J. Comput. Theor. Nanosci, 2006). Site-specific hydrogen abstraction was also demonstrated by (Hersam, Abeln et al., “An approach for efficiently locating and electrically contacting nanostructures fabricated via UHV-STM lithography on Si(100),” Microelectronic Engineering, 1999). Site-specific hydrogen donation was achieved experimentally by depositing hydrogen atoms onto a silicon surface by applying a voltage bias to a tungsten tip. (Huang and Yamamoto, “Physical mechanism of hydrogen deposition from a scanning tunneling microscopy tip,” Appl. Phys. A, 1997)
(Freitas, “Simple tool for positional diamond mechanosynthesis, and its method of manufacture,” U.S. Pat. No. 7,687,146, United States, 2010) purports to teach a tip for mechanosynthetic fabrication. However, the disclosed tip is limited to a very specific structure (a triadamantane base molecule with a dimer holder atom), performs only a single reaction (dimer deposition), and is constrained to working on a very specific surface (“having a melting point of at least 300° C., a thermal expansion coefficient maximally different than that of diamond, a mismatch in crystal lattice constant as compared to that of diamond, resistance to carbide formation, less bonding strength to the carbon dimer as compared to bonding strength between the diamond holder atom X and the carbon dimer, and little or no solubility or reaction with carbon.”) This work does not teach a versatile or generalizable system of mechanosynthesis. Additionally, it is stated that “These analyses should be repeated using ab initio techniques, and should be extended to include a calculation of activation energy barriers (which could be substantial) . . . and solvent effects . . . ” It would seem that the authors used a low level of theory in their simulations and ignored relevant chemical phenomenon, bringing into question whether the disclosed invention would actually be functional.
Subsequently, (Artyukhov, “A six degree of freedom nanomanipulator design based on carbon nanotube bundles,” Nanotechnology, 38, 2010) described a carbon nanotube-based scheme for atomically-precise tips that can also provide positioning capability. Although various possibilities are discussed as to implementing such tips, there is little detail and no clear pathway to construction.
Among other drawbacks, none of the tools described in the literature, alone or in combination, could provide a bootstrap process, a set of tools exhibiting closure (that is, a set of tools that could build themselves), a versatile set of reactions, a set of reactions of known reliability at particular temperatures, nor were they directed to a system for three-dimensional fabrication.
Literature Conflates Feedstock, Feedstock Depot, and Workpiece
As exemplified by (Oyabu, Custance et al., “Mechanical vertical manipulation of selected single atoms by soft nanoindentation using near contact atomic force microscopy,” Phys. Rev. Lett., 17, 2003; Oyabu, Custance et al., “Mechanical Vertical Manipulation of Single Atoms on the Ge(111)-c(2×8) Surface by Noncontact Atomic Force Microscopy,” Seventh International Conference on non-contact Atomic Force Microscopy, Seattle, Wash., 2004), the literature frequently uses the local presentation surface itself as what is referred to herein as the feedstock depot, the feedstock, and the workpiece. For example, in such work, atoms may be removed from the presentation surface and then added back to a void in that same presentation surface. The atoms are not being removed from the surface to transport to a workpiece distinct from the presentation surface. In these types of experiments, the local presentation surface is the source of the feedstock and it is also the workpiece which is being altered by the mechanosynthetic reactions. In addition to the limitations which may be created by conflating the feedstock, feedstock depot, and workpiece, particularly when the presentation surface is, for example, pure Si or pure Ge (thus limiting the workpiece to a single element), filling a void with a single atom is obviously not the same process as constructing a complex workpiece.
Literature Limited to One or Two Dimensions
The literature does not teach how to extend mechanosynthetically-created workpieces into three dimensions. Creating a three-dimensional structure using mechanosynthesis is not simply the extension or repetition of a one or two-dimensional motif. The bonding structure and build sequence must support extension into the third dimension through a sequence of reactions that is chemically and geometrically feasible without pathological rearrangement of intermediate products. This requires, among other things, designing build sequences which account for intermediate structures, and such strategies are not taught in the literature.
Literature Teaches Few Numbers and Types of Reactions
The number of reactions, and the variety of reactions, taught in the literature, is small. One of the most complex demonstrations of mechanosynthesis is that of (Sugimoto, Pou et al., “Complex Patterning by Vertical Interchange Atom Manipulation Using Atomic Force Microscopy,” Science, 2008), who use vertical and lateral interchange to write the letters “Si” on an Sn surface. This appears to have taken about twelve total reactions, and four different types of reactions (vertical substitution of Si for Sn, vertical substitution of Sn for Si, lateral substitution of Si for Sn, and lateral substitution of Sn for Si). (Sugimoto, Pou et al., “Complex Patterning by Vertical Interchange Atom Manipulation Using Atomic Force Microscopy,” Science, 2008) uses four types of reactions (half of which are simply the reverse reactions of the other two), employing two elements. Some other examples of previous work use more total reactions, but even less types of reactions. For example, 18-atom copper lines are made in (Lagoute, Liu et al., “Electronic properties of straight, kinked, and branchedCu/Cu(111)quantum wires: A low-temperature scanning tunneling microscopy and spectroscopy study,” Physical Review B, 12, 2006)
Literature does not Use Atomically-Precise Tips
The literature generally does not use atomically-precise tips (U.S. Pat. No. 7,687,146 is one exception that is discussed herein). For example, the tip in (Oyabu, Custance et al., “Mechanical vertical manipulation of selected single atoms by soft nanoindentation using near contact atomic force microscopy,” Phys. Rev. Lett., 17, 2003) is described as a “Si tip apex [that] was carefully cleaned up by argon-ion bombardment for 30 min.” Such a process would result in a tip where the placement of individual atoms was unknown.
Literature does not Teach Varied Tips
When contemplating numerous reactions between various elements, to create varied structures, different tips can be used to facilitate the specific reactions desired. To the best of our knowledge the literature does not address this issue.
Literature does not Provide for Specific Levels of Reaction Accuracy
The accuracy of the mechanosynthetic reactions must be considered if one is to build workpieces with a known level of reliability. The mechanosynthesis literature generally does not address the issue of designing for reaction reliability. Some literature reports the reliability of a given reaction after the fact based on experimental results, but this is different than engineering the system ahead of time so that the reactions achieve a desired level of accuracy. For example, (Sugimoto, Pou et al., “Complex Patterning by Vertical Interchange Atom Manipulation Using Atomic Force Microscopy,” Science, 2008) provides computer modeling of a reaction barrier in rationalizing the observed behavior of their experimental system. But, this analysis is post-facto. The authors did not attempt to design a system ahead of time with a known level of reliability.
Further, as previously noted, the literature generally uses atomically-imprecise tips. Even where modeling is performed in the literature, modeling of an atomically-imprecise tip is unlikely to accurately represent the actual experimental system due to lack of knowledge of the exact structure of the tip. For example, the reaction modeling done in (Sugimoto, Pou et al., “Complex Patterning by Vertical Interchange Atom Manipulation Using Atomic Force Microscopy,” Science, 2008) used a simplified tip structure which is almost certainly not the structure that was actually used experimentally.
Obviously, since the literature is not directed to a system with a planned level of reliability, neither does the literature investigate reaction reliability across a range of tips, elements, or conditions to teach a generalizable system for not only building workpieces, but building them with a known level of confidence.
Literature not Using Individual Atoms or Molecules
    [1] The wording of the literature is not always clear as to when atoms are being referred to, versus some larger (and often indistinctly-defined) building block. Terminology used in the literature includes “cluster,” “nanoparticle,” “nanoscale object,” “particle” and “nodule,” among other terms. Regardless of the terminology used, work using imprecisely-defined building blocks is not an appropriate parallel to positioning, and making or breaking bonds, with atomic precision.
Perhaps even more confusing, literature exists which attempts to conflate atoms, molecules, and large, indistinct clusters of atoms. For example, (Ramachandran, Baur et al., “Direct and Controlled Manipulation of Nanometer-Sized Particles Using the Non-Contact Atomic Force Microscope,” Nanotechnology, 9, 1998) defines “nanoscale objects” as essentially anything under one micron in diameter, including atoms, molecules, dendrimers, macro-molecules, viruses, phages, colloids, clusters, nanoparticles, nano-devices and other fabricated structures. [Col 6, Lines 61-67] Such a definition would include objects containing billions of atoms, where the placement of individual atoms is not known.
Clearly, mechanosynthesis cannot, at least in a planned manner that results in an atomically-precise workpiece, be performed using workpiece or feedstock structures in which the location of the constituent atoms is unknown.
Literature on Automated Mechanosynthesis
(Celotta, Balakirsky et al., “Invited Article: Autonomous assembly of atomically perfect nanostructures using a scanning tunneling microscope,” Rev Sci Instrum, 12, 2014) describes the automated creation of two-dimensional structures. Chemistry is limited to an atomically-imprecise Iridium tip, and either Co atoms or CO molecules as feedstock. “Path planning” is used, which is limited to two dimensions. Feedstock is dragged across the surface to its desired location, rather than being picked up, moved, and then deposited, eliminating the possibility of building three dimensional structures. Further, the nature of the bonds being formed is unclear; it seems likely that the two-dimensional structures formed are physically adsorbed, not chemically bonded.
Non-Atomically-Precise Products
Many other ways of building chemical structures exist. However, other such methods, not being able to create a wide range of atomically-precise structures, generally do not result in the same products.
For example, it is well-known that CVD (Chemical Vapor Deposition) can be used to create multi- or single-crystal diamond or other materials. However, such materials, being the result of stochastic processes rather than individually-placed atoms, generally contain impurities, vacancies, incorrectly bonded atoms (e.g., sp2 versus sp3 hybridized carbon in the case of diamond), and random grain boundaries or overall product boundaries. And, a simple crystal is the best-case scenario for techniques like CVD. Most atomically-precise, non-periodic structures would be impossible to create using stochastic techniques.
An atomically-precise product generally has markedly different characteristics than a similar product which is not atomically-precise. For example, with respect to bulk material properties, strength and heat conductivity generally increase with atomic-precision.
Summary of Literature
    [2] The literature teaches the ability to make and break bonds using a small set of elements, with a limited set of reactions, only to specific structures (such as the 7×7 reconstruction of Silicon, or other similarly-specific and limited environments), using only the top atomic layer of a presentation surface. Additionally, the experimental mechanosynthetic reactions found in the literature have not been engineered in advance for versatility or reliability. Reliability, while a minor issue when, for example, the goal is to simply interchange one atom for another on a surface, becomes important when the goal is to reliably build atomically-precise structures containing many atoms or requiring many reactions.
Another drawback of the literature is that the presentation surface also frequently serves as the feedstock depot, feedstock and workpiece, such as with the “vertical manipulation” literature, of which (Oyabu, Custance et al., “Mechanical vertical manipulation of selected single atoms by soft nanoindentation using near contact atomic force microscopy,” Phys. Rev. Lett., 17, 2003; Oyabu, Custance et al., “Mechanical Vertical Manipulation of Single Atoms on the Ge(111)-c(2×8) Surface by Noncontact Atomic Force Microscopy,” Seventh International Conference on non-contact Atomic Force Microscopy, Seattle, Wash., 2004) are representative. Without more separation of the presentation surface, feedstock and workpiece, the ability to create diverse structures can be limited.
Drawbacks are also created by the use of non-atomically-precise tips in the literature, and in some cases, unrealistically-low levels of theory in computational simulations. Further, the literature contains no teachings as to how one might generalize the mechanosynthetic techniques presented to other elements and reactions, or to construct complex, three-dimensional workpieces.
Overall, the literature is directed towards viewing mechanosynthesis as a very limited set of surface modifications, not as a generalizable set of concepts, tools, reactions and procedures designed for reliably building varied workpieces. The present invention addresses all of these issues, as will be seen from the detailed explanations and exemplary embodiments.
With respect to mechanosynthetic products rather than processes, the ability to create atomically-precise structures, whether crystalline, quasi-crystalline, or non-periodic, gives rise to products with different or superior characteristics that generally cannot be fabricated using other known methods.